If she's forward facing then she has already outgrown her current seat & needs it replaced immediately
Also, it is not recommended to buy used carseats -- unless the eBay seller is a Certified Child Passenger Safety Technician, then I would not trust their carseat.... It's puting your child's life in the care of a perfect stranger
You can't know if it has suffered a crash, if it's missing pieces, if it's expired, if the harness straps have been submerged in water or ironed, etc.
- What is your daughter's age, weight & height?
- What is your budget?
- What year is your vehicle?
Maybe we can help you narrow down some safe affordable options